In gas turbine engines, air is compressed at an initial stage, then is heated in combustion chambers, and the hot gas so produced passes to a turbine that, driven by the hot gas, does work which may include rotating the air compressor.
In a typical industrial gas turbine engine a number of combustion chambers combust fuel and hot gas flowing from these combustion chambers is passed via respective transitions (also referred to by some in the field as ducts) to respective entrances of the turbine. More specifically, a plurality of combustion chambers commonly are arranged radially about a longitudinal axis of the gas turbine engine, and likewise radially arranged transitions comprise outlet ends that converge to form an annular inflow of hot gas to the turbine entrance. Each transition exit is joined by a seal to one or more turbine components, which in various designs are known as row 1 vane segments. Adjacent component growth variances due to thermal expansion, thermal stresses, and vibrational forces from combustion dynamics all affect design criteria and performance of such a seal, referred to herein as a transition-to-turbine seal. Consequently, the design of such seal has presented a challenge that resulted in various approaches that attempt to find a suitable balance between seal cost, reliability, durability, installation and repair ease, performance, and effect on adjacent components.
For example, U.S. Pat. No. 5,265,412, issued Nov. 30, 1993 to Bagepalli et al., teaches the use of flexible brush seals that are positioned between the transition and turbine entrance. An exemplary embodiment comprises a sealing cap solidly affixed to a first stage nozzle of the turbine, extending over a brush seal positioned at the end of the transition and an extending flexible brush radially outward to contact the adjacent sealing cap. An alternative embodiment provides the brush on the turbine component and the sealing cap extending from the transition (see FIG. 8). U.S. Pat. No. 5,749,218, issued May 12, 1998 to Cromer and Potter, illustrates a prior art flexible seal, one end of which fits into a U-shaped slot in the transition. The other end engages the first stage of the turbine. Recognizing a problem of wear in the U-shape slot, the '218 inventors solve this problem by inserting an insert into the slot that is comprised of a harder alloy than the metal forming the slot. This is stated to increase the effective wear resistance of the slot.
A number of other seal design approaches involve spring-loaded or formed seals, some with felt metal inserts. However, these are considered to involve unacceptable risks of failure or excessive wear, and/or difficulties with installation.
Each of the known approaches to transition-to-turbine seals has one or more factors that argue against its use in more advanced-design gas turbine engines. Thus, there remains a need for an improved transition-to-turbine seal.